Fire-resistant alloy with high electric resistance



Patented June 11, 1929 1 UNITED STATES- 1,717,284 PATENT OFFICE.

HANS GUSTAF ALBERT VON KANTZOW, OF HALLSTAHAMMAR, SWEDEN.

FIRE-RESISTANT ALLOY WITH HIGH ELECTRIC RESISTANCE.

No Drawing. Application filed December 19, 1927, Serial No. 241,259, and in- Sweden December 15, 1926.

It is previously known that alloys containing iron and aluminium, or iron, aluminium and chromium and/or manganese are fire resistant at higher temperatures if the percent- 5 age ofaluminium is relatively high, for instance at least 12%, and that the electric resistance of such alloys is also, especially at higher temperatures, rather high. Such alloys can be worked, for instance rolled or 10 drawn, if the percentage of aluminium is not too high (generally not over 16%), but only with great difiiculty.

It has nowbeen found, that the said qualities of alloys of the kind described can be greatly improved by an addition of relatively small quantities of cobalt, for instance not over 6%, and generally in quantities varying between 1 and 4%. The same results can be obtained if, instead of cobalt alone, a mixture of cobalt and titanium be introduced into such alloys.

The present invention therefore relates to alloys containing as principal constituents iron and aluminium, or iron, aluminium and chromium or manganese or both, in which the percentage of aluminium is 05-14%, the percentage of chromium is any percentage up to 30% and the percentage of manganese is any percentage up to 12%, and-the novel feature of the invention consists in this that alloys of the kind described also contain a relativel small percentage, say at most 36%, 0 cobalt or of cobalt and titanium together. Moreover, said alloys may also contain as secondary constituents substances which are generally present in densified iron, such as Si. The said small quantities of cobalt are used principally from economical reasons.

Practical tests have shown that by such an addition of cobalt alone or together with titanium to alloys of the kind set forth, especially those containing chromium, the fire resistance will be raised by several hundred per cent, and that the electric resistance will also be considerably raised, for instance by about or more. At the same time the advantage is gained that the percentage of aluminium required in such alloys can be considerably reduced below the above mentioned minimum limit. Finally the possibiL- ity of working such alloy byrolling, drawing etc. will, although the fire resistance and the electric resistance are so much raised, be maintained.

Hitherto it has been considered that subsame time present in the iron more than one alley occurs in the same.

It has been found that the best results are obtained b the following compositions of the iron a loy: Al 15%, Co 1-6% or Al 1-5%, Cr 522% and C0 1-4%. It is to be understoodthat although only the minimum and maximum limits of the percentages are mentioned the invention covers any percentages between the same.

EXAMPLES.

For the sake of clearness the electric resistance and the fire resistance are indicated in different examples.

Electric resistance.

1. An iron alloy with at most 0.35% of carbon and 6% of Al had at 18 C. an electric resistance of 84 microhm per em After an addition of 2% of Co said resistance was raised to microhm and after an addition of 6% of Co said resistance was 97 microhm per cm.

2. An iron alloy containing 1% of Al and 18% 'of Cr had' at 18 C." an electric resistance of 84 microhm per em After an addition of 2% of Co to such alloy the electric resist-- ance was 99.8 microhm.

3. An iron alloy containing 4.5% of Al and 18% of Cr had at 18 C. an electric resistance of microhm per em After an addition of 2% Co to such alloy the said resistance was raisedto microhm per cm".

Fire resistance.

4. An iron alloy containing 10% of Al lost after 6 hours heatin at 1000 C. about 0.9% of its weight and a ter 6 hours heating at 1100 C. theloss in weight was 1.5%.

5. An iron alloy containing 4% of Al and 2% ofCo had after 6 hours heating at 1000 C. lostabout 0.5% of its original weight.

6. An iron alloy containing 18% of Cr and 5% of Al lost after 6 hours heating at 1100 C. about 0.7% of its weight and after *6 hours heating at 11501200 G. the loss in weight was 1.1%.-

7. An iron alloy containing 18% of Cr, 4% of Al (consequently 1% less than in Example-4;) and 2% of Co lost after 6 hours heating at 1100 C. about 0.05% of its weight and after 6 hours heating at 1150-1200 C. the loss in weight was about 0.07%.

Due to the above mentioned properties the ing res1stances,especially for high tempera tures.

Hitherto the so called nichrome has generally been .used for such purposes. The nichrome is an alloy principally containing nickel (62-89%), chromium (11-35%) and iron (023%). The nichrome has a high electric resistance and is very fire resistant, but is very diflicult to work as well at ordinary as at higher temperatures. From this reason and due to the metals contained in the nichrome electric resistances and other objects made from the same are very expensive.

The present invention makes it possible to obtain alloys having in most cases better properties than those of the nichrome, to a considerably lower price than that of the latter.

The hitherto executed tests seem to make clear that it is important for the fire resistance that the material has no determined critical points within the range of higher temperatures within which the material is generally to be heated, so that no re-crystallization will take place. Any re-crystalliza tion Will easily break the material, the breaking action being the more vigorous the more often the heating is repeated.

I claim: v

1. A fire resistant alloy havinga high electric resistance containing as principal constituents iron, 0.544% of aluminium, an appreciable amount up to 30% of chromium and 0.56% of cobalt.

2. A fire resistant alloy having a high electric resistance containing. as principal constituents iron, 0.5-14l% of aluminium, an appreciable amount up to 30% of chromium and 0.56%- of cobalt and titanium.

3. A fire resistant alloy having a high electric resistance containing as principal constituents iron with at most 0.35% of carbon, 0.544% of aluminium, 522% of chromium and 13% of cobalt.

In testimony whereof I have hereunto affixed my signature.

HANS GUSTAF ALBERT von KANTZOW. 

